Organic sulfur material, electrode, and lithium-ion secondary batteries, and producing method

ABSTRACT

It is an object of the present invention to provide a novel organic sulfur material which is capable of improving a charge/discharge capacity and cycle characteristics, an electrode comprising the organic sulfur material, that is, a positive electrode or a negative electrode, and a lithium-ion secondary battery comprising the electrode. Provided is an organic sulfur material comprising a sulfur-modified acrylic resin, wherein an acrylic resin has peaks around 756 cm −1 , around 1066 cm −1 , around 1150 cm −1 , around 1245 cm −1 , around 1270 cm −1 , around 1453 cm −1 , and around 1732 cm −1  in an FT-IR spectrum.

TECHNICAL FIELD

The present invention relates to a novel organic sulfur material, anelectrode comprising the organic sulfur material, and a lithium-ionsecondary battery comprising the electrode, and a producing methodthereof.

BACKGROUND OF THE INVENTION

Since the lithium-ion secondary battery has a large charge/dischargecapacity, it has been mainly used as a battery for a portable electronicdevice. In addition, an increasing amount of the lithium-ion secondarybattery has been used as a battery for an electric vehicle and has beenexpected to improve in performance.

WO 2010/044437 describes a positive electrode active material for alithium-ion secondary battery obtained by heating a raw material powdercomprising a sulfur powder and a polyacrylonitrile powder under anon-oxidizing atmosphere. Moreover, J P 2015-092449 A aims to provide apositive electrode active material at low cost by using an industrialrubber.

On the other hand, for a negative electrode active material, it has beenproposed to increase a battery capacity of the lithium-ion secondarybattery by using a material, such as silicon (Si) and tin (Sn), that canocclude and release more lithium ions.

SUMMARY OF THE INVENTION

However, the positive electrode active material in WO 2010/044437 has aproblem that it is difficult to provide a lithium-ion secondary batteryat low cost, since polyacrylonitrile, which is a raw material, isexpensive, in particular, polyacrylonitrile with stable quality is moreexpensive. The positive electrode active material in JP 2015-092449 Astill has a problem in sufficiently improving cycle characteristics. Theabove-described material that has been proposed as a negative electrodeactive material has a problem that the cycle characteristics whenrepeatedly charging and discharging is not good because a volume changedue to occlusion and release of lithium ions is large. In addition,though carbon materials such as graphite and hard carbon are also used,the theoretical capacity has been almost reached already, and asignificant capacity improvement cannot be expected.

It is an object of the present invention to provide a novel organicsulfur material which is capable of improving a charge/dischargecapacity and cycle characteristics of a lithium-ion secondary battery,an electrode comprising the organic sulfur material, that is, a positiveelectrode or a negative electrode, and a lithium-ion secondary batterycomprising the electrode, and a producing method thereof.

As a result of intensive studies to solve the above-described problem,the present inventors have found that if a predetermined acrylic resinis modified with sulfur, an organic sulfur material which exhibitsexcellent characteristics can be obtained, and conducted further studiesto complete the present invention.

That is, the present invention relates to

[1] An organic sulfur material comprising:

a sulfur-modified acrylic resin,

wherein an acrylic resin has peaks around 756 cm⁻¹, around 1066 cm⁻¹,around 1150 cm⁻¹, around 1245 cm⁻¹, around 1270 cm⁻¹, around 1453 cm⁻¹,and around 1732 cm⁻¹ in an FT-IR spectrum,

[2] The organic sulfur material of [1] above, wherein the peak around1150 cm⁻¹ and the peak around 1732 cm⁻¹ are larger than the remainingpeaks,

[3] The organic sulfur material of [1] or [2] above, wherein the FT-IRspectrum further has peaks around 846 cm⁻¹, around 992 cm⁻¹, around 1196cm⁻¹, around 2955 cm⁻¹, and around 2996 cm⁻¹,

[4] The organic sulfur material of any one of [1] to [3] above, whereinmass ratios of carbon, hydrogen, nitrogen, and sulfur in a total amountof the acrylic resins are 60.0 to 70.0%, 7.5 to 9.5%, 0.0%, and 0.0 to1.0%, preferably 60.0 to 69.0%, 7.6 to 9.4%, 0.0%, and 0.0 to 0.9%, morepreferably 60.0 to 68.0%, 7.7 to 9.3%, 0.0%, and 0.0 to 0.8%, furtherpreferably 60.0 to 67.0%, 7.7 to 9.2%, 0.0%, and 0.0 to 0.7%, furtherpreferably 60.0 to 67.0%, 7.7 to 9.2%, 0.0%, and 0.0 to 0.6%, furtherpreferably 60.5 to 66.5%, 7.7 to 9.2%, 0.0%, and 0.0 to 0.5%,respectively,

[5] The organic sulfur material of any one of [1] to [4] above, whereinthe modification is performed by calcination under a non-oxidizingatmosphere,

[6] The organic sulfur material of any one of [1] to [5] above, whereina particle size of the acrylic resin is 0.1 to 300.0 μm, preferably 1.0to 270.0 μm, more preferably 1.0 to 200.0 μm, further preferably 1.0 to100.0 μm, further preferably 1.0 to 50.0 μm, further preferably 1.0 to20.0 μm, further preferably 1.0 to 15.0 μm,

[7] The organic sulfur material of any one of [1] to [6] above, whereinthe acrylic resin has a porous structure,

[8] The organic sulfur material of any one of [1] to [7] above, wherein,in a Raman spectrum detected by Raman spectroscopy, there exists a mainpeak around 1450 cm⁻¹, and there exists other peaks around 485 cm⁻¹,around 1250 cm⁻¹, and around 1540 cm⁻¹ in a range of 200 to 1800 cm⁻¹,

[9] The organic sulfur material of [8] above, wherein, in the Ramanspectrum, with a straight line connecting an intensity of 1000 cm⁻¹ andan intensity of 1800 cm⁻¹ being as a baseline, when a difference (I₁₄₅₀)between a peak intensity around 1450 cm⁻¹ and a corresponding baselineintensity and a difference (I₁₅₄₀) between a peak intensity around 1540cm⁻¹ and a corresponding baseline intensity are calculated, a value ofI₁₄₅₀/I₁₅₄₀ is in a range of 1 to 4,

[10] The organic sulfur material of any one of [1] to [9] above, whereinan amount of sulfur in the organic sulfur material is 50.0% by mass ormore, more preferably 53.0% by mass or more, further preferably 55.0% bymass or more, further preferably 56.0% by mass or more,

[11] An electrode comprising the organic sulfur material of any one of[1] to [10] above,

[12] A lithium-ion secondary battery comprising the electrode of [11]above,

[13] A method of producing an organic sulfur material, the methodcomprising steps of

(1) preparing an acrylic resin, and

(2) modifying the acrylic resin with sulfur,

wherein the acrylic resin has peaks around 756 cm⁻¹, around 1066 cm⁻¹,around 1150 cm⁻¹, around 1245 cm⁻¹, around 1270 cm⁻¹, around 1453 cm⁻¹,and around 1732 cm⁻¹ in an FT-IR spectrum,

[14] The method of [13] above, wherein the modification is performed bycalcination under a non-oxidizing atmosphere,

[15] The method of [13] or [14] above, wherein an amount of sulfur withrespect to the acrylic resin is 50 to 1000 parts by mass, preferably 100parts by mass to 750 parts by mass, more preferably 150 parts by mass to500 parts by mass, further preferably 200 parts by mass to 500 parts bymass, further preferably 250 parts by mass to 500 parts by mass, basedon 100 parts by mass of the acrylic resin,

[16] The method of [14] or [15] above, wherein a temperature of thecalcination is 250 to 550° C., preferably 300° C. to 500° C., morepreferably 300° C. to 450° C. or lower,

[17] The method of any one of [13] to [16] above, wherein a particlesize of the acrylic resin is 0.1 to 300.0 μm, preferably 1.0 to 270.0μm, more preferably 1.0 to 200.0 μm, further preferably 1.0 to 100.0 μm,further preferably 1.0 to 50.0 μm, further preferably 1.0 to 20.0 μm,further preferably 1.0 to 15.0 μm,

[18] The method of any one of [13] to [17] above, wherein the acrylicresin has a porous structure,

[19] A method of producing an electrode, the method further comprising,after producing the organic sulfur material by the method of any one of[13] to [18] above, a step of:

(3) preparing an electrode using the organic sulfur material by aconventional method,

[20] A method of producing a lithium-ion secondary battery, the methodfurther comprising, after producing the electrode by the method of [19]above, a step of:

(4) preparing a lithium-ion secondary battery using the electrode by aconventional method.

According to the present invention, a novel organic sulfur materialwhich is capable of improving charge/discharge capacity and cyclecharacteristics, an electrode comprising the organic sulfur material,that is, a positive electrode or a negative electrode, and a lithium-ionsecondary battery comprising the electrode can be provided.

In the present specification, the “cycle characteristics” refers tocharacteristics of maintaining charge/discharge capacity of a secondarybattery despite repeated charging/discharging. Therefore, a secondarybattery having a large degree of decrease in charge/discharge capacityand a low capacity retention with the repeated charging/discharging isinferior in cycle characteristics, while on the other hand, a secondarybattery having a small degree of decrease in charge/discharge capacityand a high capacity retention is excellent in cycle characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematically shown cross-sectional view of a reactionapparatus used for producing an organic sulfur material in Examples.

FIG. 2 parallelly shows profiles of FT-IR spectra of the acrylic resinsused in Examples 1 to 4 under the same horizontal axis (wave number(cm⁻¹)) so that their peak positions can be compared.

FIG. 3 parallelly shows profiles of Raman spectra for the organic sulfurmaterials in Example 1 and Comparative examples 1 and 2 under the samehorizontal axis (Raman shift (cm⁻¹)) so that their peak positions can becompared.

FIG. 4 represents a profile of each Raman spectrum in FIG. 3 so that avalue of I₁₄₅₀/I₁₅₄₀ can be grasped on a graph. Here, I₁₄₅₀ is adifference between a peak intensity around 1450 cm⁻¹ and a correspondingbaseline intensity (A in the figure), and I₁₅₄₀ is a difference betweena peak intensity around 1540 cm⁻¹ and a corresponding baseline intensity(B in the figure). Besides, the baseline is a straight line drawn almosthorizontally in the figure and connecting an intensity of 1000 cm⁻¹ andan intensity of 1800 cm⁻¹ in each profile.

DETAILED DESCRIPTION

Hereinafter, a structure of the present disclosure will be described indetail. Besides, a numerical value of an upper limit relating to “orless (lower)” or “to” and a numerical value of a lower limit relating to“or more (higher)” or “to” with respect to description of a numericalrange are numerical values which can be arbitrarily combined, and anumerical value in Examples can also be used as an upper or a lowerlimit. In addition, a numerical range identified with “to” means toinclude the numerical values of both ends, unless otherwise specified.

One embodiment of the present disclosure is an organic sulfur material,the organic sulfur material being obtained by modifying an acrylic resinwith sulfur, wherein the acrylic resin has peaks around 756 cm⁻¹, around1066 cm⁻¹, around 1150 cm⁻¹, around 1245 cm⁻¹, around 1270 cm⁻¹, around1453 cm⁻¹ and around 1732 cm⁻¹ in an FT-IR spectrum.

Another embodiment of the present disclosure is an electrode comprisingthe organic material.

Another embodiment of the present disclosure is a lithium-ion secondarybattery comprising the electrode.

Another embodiment of the present disclosure is a method of producing anorganic sulfur material, the method comprising steps of:

(1) preparing an acrylic resin, and

(2) modifying the acrylic resin with sulfur,

wherein the acrylic resin has peaks around 756 cm⁻¹, around 1066 cm⁻¹,around 1150 cm⁻¹, around 1245 cm⁻¹, around 1270 cm⁻¹, around 1453 cm⁻¹and around 1732 cm⁻¹ in an FT-IR spectrum.

Another embodiment of the present disclosure is a method of producing anelectrode, the method further comprising, after producing the organicsulfur material by the method above, a step of:

(3) preparing an electrode using the organic sulfur material by aconventional method.

Another embodiment of the present disclosure is a method of producing alithium-ion secondary battery, the method further comprising, afterproducing the electrode by the method above, a step of:

(4) preparing a lithium-ion secondary battery using the electrode by aconventional method.

<Acrylic Resin>

In the present disclosure, the acrylic resin has peaks around 756 cm⁻¹,around 1066 cm⁻¹, around 1150 cm⁻¹, around 1245 cm⁻¹, around 1270 cm⁻¹,around 1453 cm⁻¹, and around 1732 cm⁻¹ in an FT-IR spectrum.

In the acrylic resin, the peaks around 1150 cm⁻¹ and a peak around 1732cm⁻¹ are preferably larger than the remaining peaks from the viewpointof the effects of the present disclosure.

It is more preferable that the acrylic resin further has peaks around846 cm⁻¹, around 992 cm⁻¹, around 1196 cm⁻¹, around 2955 cm⁻¹ and around2996 cm⁻¹ in the FT-IR spectrum, from the viewpoint of the effects ofthe present disclosure.

In the present disclosure, the FT-IR spectrum can be measured by thetotal reflection method under a condition of a resolution of 4 cm⁻¹, acumulative number of 10 times, and a measurement range of 400 cm⁻¹ to4000 cm⁻¹, using a Fourier transform infrared spectrophotometer(IRAffitity-1) manufactured by Shimadzu Corporation. FIG. 2 parallellyshows profiles of the FT-IR spectra of the acrylic resins used inExamples 1 to 4 under the same horizontal axis (wave number (cm⁻¹)) sothat their peak positions can be compared with each other. With respectto the peak positions of the FT-IR spectra, “around” means allowing anerror range of ±10 cm⁻¹, particularly ±5 cm⁻¹.

Mass ratios of carbon, hydrogen, nitrogen, and sulfur in a total amountof the acrylic resin are preferably in a range of 60.0 to 70.0%, 7.5 to9.5%, 0.0% and 0.0 to 1.0%, respectively, from the viewpoint of theeffects of the present disclosure. Here, the mass ratio of carbon ismore preferably 60.0 to 69.0%, further preferably 60.0 to 68.0%, furtherpreferably 60.0 to 67.0%, further preferably 60.5 to 66.5%. The massratio of hydrogen is more preferably 7.6 to 9.4%, more preferably 7.7 to9.3%, further preferably 7.7 to 9.2%. The mass ratio of nitrogen is0.0%. The mass ratio of sulfur is more preferably 0.0 to 0.9%, furtherpreferably 0.0 to 0.8%, further preferably 0.0 to 0.7%, furtherpreferably 0.0 to 0.6%, further preferably 0.0 to 0.5%.

In the present disclosure, a mass ratio of an element constituting anacrylic resin can be measured by the similar method as an elementalanalysis for an organic sulfur material which will be described later.

Examples of the acrylic resin include a polymer of poly (meth)acrylicalkyl ester, a copolymer of (meth)acrylic alkyl ester and alkyleneglycol di(meth)acrylate, and the like. Here, “(meth)acrylate” representseither “acrylate” or “methacrylate” (the same shall apply hereinafter).

Preferred examples of the acrylic resin without limitation include ahomopolymer of methyl (meth)acrylate, a homopolymer of butyl(meth)acrylate, a copolymer of methyl (meth)acrylate and ethylene glycoldi(meth)acrylate, a copolymer of butyl (meth)acrylate and ethyleneglycol di(meth)acrylate, and the like. Among them, as the acrylic resin,a methacrylate type of acrylic resin is preferable. Further preferredexamples of the acrylic resin include a copolymer of butyl methacrylateand ethylene glycol dimethacrylate.

The acrylic resin can be used alone or two or more thereof can be usedin combination.

(Form of Acrylic Resin)

In the present disclosure, the acrylic resin is preferably in a form ofa fine particle. Here, the fine particle refers to a particle having aparticle size of 300.0 μm or less. The particle size is preferably 270.0μm or less, more preferably 200.0 μm or less, further preferably 100.0μm or less, further preferably 50.0 μm or less, further preferably 20.0μm or less, further preferably 15.0 μm or less, further preferably 13.0μm or less, further preferably 10.0 μm or less, further preferably 6.0μm or less. On the other hand, a lower limit of the particle size is notparticularly limited, but is usually, for example, 0.1 μm or more,preferably 1.0 μm or more. The particle size is a value measured by aprecise particle size distribution measuring device, Multisizer 3manufactured by Beckman Coulter, Inc.

The acrylic resin may be a spherical fine particle or a porous fineparticle. When the acrylic resin is a porous fine particle, an oilabsorption amount thereof is preferably 100 ml/100 g or more, morepreferably 110 ml/100 g or more, further preferably 120 ml/100 g ormore, further preferably 130 ml/100 g or more, further preferably 140ml/100 g or more. The oil absorption amount is a value measuredaccording to JIS K 5101-13-2: 2004. More specifically, it can bemeasured by the method in Paragraph 0069 of JP 2017-88501 A.

(Weight-Average Molecular Weight (Mw) of Acrylic Resin)

A Mw of the acrylic resin is not particularly limited as long as theacrylic resin has the above-described structure. However, the Mw of theacrylic resin is usually in a range of 2000 to 1500000. The Mw is avalue measured by gel permeation chromatography (GPC) (calibrated withpolystyrene).

(Availability or Producing of Acrylic Resin)

The acrylic resin is commercially available or can be produced by aconventional method which is within a knowledge of a person skilled inthe art. Examples of the commercially available acrylic resin include,for example, those manufactured by Sekisui Kasei Co., Ltd. and SekisuiChemical Co., Ltd.

<Sulfur>

As sulfur, those in various forms such as a powdered sulfur, aninsoluble sulfur, a precipitated sulfur, and a colloidal sulfur can beused. Among them, a precipitated sulfur and a colloidal sulfur arepreferable. A compounding amount of sulfur is preferably 50 parts bymass or more, more preferably 100 parts by mass or more, furtherpreferably 150 parts by mass or more, further preferably 200 parts bymass or more, further preferably 250 parts by mass or more, based on 100parts by mass of the acrylic resin. When it is 100 parts by mass ormore, the charge/discharge capacity and cycle characteristics tend to beimproved. On the other hand, the compounding amount of sulfur is notparticularly limited, but is usually 1000 parts by mass or less,preferably 750 parts by mass or less, more preferably 500 parts by massor less, further preferably 400 parts by mass or less, furtherpreferably 350 parts by mass or less. When it is 1000 parts by mass orless, there is a tendency that it is advantageous in terms of cost.

<Conductive Carbon Material>

When the acrylic resin is modified with sulfur, a conductive carbonmaterial may be added to the acrylic resin in advance. This is becausethe conductivity of the organic sulfur material can be improved. As sucha conductive carbon material, a carbon material having a graphitestructure is preferable. As the carbon material, one having a condensedaromatic ring structure such as, for example, carbon black, acetyleneblack, ketjen black, graphite, carbon nanotube (CNT), carbon fiber (CF),graphene, and fullerene can be used. The conductive carbon material canbe used alone or two or more thereof can be used in combination.

Among them, acetylene black, carbon black, and ketjen black arepreferable because they are inexpensive and excellent in dispersibility.Moreover, a small amount of CNT, graphene or the like may be used incombination with acetylene black, carbon black, or ketjen black. Withsuch combination, it becomes possible to further improve the cyclecharacteristics of the lithium-ion secondary battery withoutsignificantly increasing the cost. Besides, the amount of CNT orgraphene used in combination is preferably 8% by mass or more and 12% bymass or less of a total amount of the conductive carbon material.

A compounding amount of the conductive carbon material is preferably 5parts by mass or more, more preferably 10 parts by mass or more, basedon 100 parts by mass of the acrylic resin. When the compounding amountis 5 parts by mass or more, there is a tendency to easily achieve thepurpose of further improving the charge/discharge capacity and the cyclecharacteristics. On the other hand, the compounding amount is preferably50 parts by mass or less, more preferably 40 parts by mass or less. Whenit is 50 parts by mass or less, there is a tendency to easily achievethe purpose of further improving the charge/discharge capacity and cyclecharacteristics without relatively decreasing a ratio of a structurecomprising sulfur in the organic sulfur material.

<Other Materials>

When the acrylic resin is modified with sulfur, other materials usuallyused in this field may be added to the acrylic resin in advance, ifdesired.

<Production of Organic Sulfur Material>

In the present disclosure, the organic sulfur material can be producedby modifying a predetermined acrylic resin with sulfur.

(Preparation of Raw Material)

For modification, it is desirable that an acrylic resin and sulfur aresufficiently mixed in advance. Where a conductive carbon material andthe like are added to the acrylic resin in advance, these additives arealso mixed together. The mixing can be performed by a conventionalmethod using, for example, a high-speed blender or the like. On theother hand, an acrylic resin, sulfur, and, if desired, additives can bemolded in a pellet-shape.

(Non-Oxidizing Atmosphere)

The modification is preferably performed under a non-oxidizingatmosphere. The non-oxidizing atmosphere refers to an atmosphere thatdoes not substantially comprise oxygen and is adopted to suppressoxidative deterioration and excessive thermal decomposition ofconstituents. Specifically, it refers to an atmosphere of an inert gassuch as nitrogen or argon, an atmosphere of sulfur gas, or the like.Therefore, the modification is performed, for example, in a quartz tubeunder an inert gas atmosphere.

(Modification Method)

Modification of acrylic resin with sulfur can be performed by aconventional method, for example, by calcinating an acrylic resin andsulfur. The calcination can be performed by a conventional method. Forexample, the calcination can be performed by heating a calcinating rawmaterial (including an acrylic resin, sulfur, and, if desired,additives) at a predetermined temperature rising rate until reaching apredetermined temperature, maintaining them at the predeterminedtemperature for a predetermined period of time, and then naturallycooling them.

[Temperature Rising Rate]

A temperature rising rate is preferably in a range of, for example, 50to 500° C./h. The temperature rising rate is more preferably 100° C./hor higher. On the other hand, the temperature rising rate is morepreferably 400° C./h or lower, further preferably 300° C./h or lower,further preferably 200° C./h or lower. When the temperature rising rateis within such ranges, there is a tendency to easily achieve the purposeof improving the charge/discharge capacity and the cyclecharacteristics.

[Calcinating Temperature/Time]

The calcinating temperature is a temperature after completion oftemperature rise and to be maintained for a certain period of time forcalcinating a raw material. The temperature is preferably in a range of250 to 550° C. When the temperature is 250° C. or higher, aninsufficient vulcanization reaction can be avoided, and there is atendency that a decrease in charge/discharge capacity of an objectivematerial can be prevented. On the other hand, when the temperature is550° C. or lower, decomposition of a calcinated raw material isprevented, and there is a tendency that a decrease in yield and adecrease in charge/discharge capacity can be prevented. The temperatureis more preferably 300° C. or higher, further preferably 350° C. orhigher. On the other hand, the temperature is more preferably 500° C. orlower, more preferably 450° C. or lower. A time for maintaining at acalcinating temperature may be appropriately set according to a type ofa calcinating raw material, a calcinating temperature, etc., but ispreferably 1 to 6 hours, for example. When it is 1 hour or more, thereis a tendency that calcination can be proceeded sufficiently, and whenit is 6 hours or less, there is a tendency that excessive thermaldecomposition of the constituents can be prevented.

[Apparatus]

Calcination can be performed by using an apparatus shown in FIG. 1, aswell as, for example, a continuous type apparatus such as a twin-screwextruder. When the continuous type apparatus is used, there is anadvantage that an organic sulfur material can be continuously producedby a series of operations, such as by kneading, pulverizing and mixing araw material with calcination in the apparatus.

(Step of Removing Residue)

Unreacted sulfur which was precipitated by cooling from sulfursublimated during calcination, etc., remain in a processed productobtained after calcination. It is desirable to remove these residues asmuch as possible because they cause deterioration in cyclecharacteristics. The removal of the residues can be performed accordingto a conventional method such as pressure reduced heat drying, warm airdrying, and solvent washing.

(Pulverization, Classification)

The obtained organic sulfur material can be pulverized so as to have apredetermined particle size and classified into a particle having a sizesuitable for producing an electrode. A preferred particle sizedistribution of the particle is about 5 to 40 μm in median diameter.Besides, in the calcinating method using the twin-screw extruderdescribed above, pulverization of the produced organic sulfur materialcan be performed by shearing during kneading at the same time asproduction of the organic sulfur material.

<Organic Sulfur Material>

The organic sulfur material thus obtained comprises carbon and sulfur asmain components, and the larger the amount of sulfur is, the better thecharge/discharge capacity and cycle characteristics tend to improve.Therefore, it is preferable that the content of sulfur is as high aspossible. Generally, a range of the amount of sulfur is preferably 50.0%by mass or more, more preferably 53.0% by mass or more, furtherpreferably 55.0% by mass or more, further preferably 56.0% by mass ormore, in the organic sulfur material. However, when a conductive carbonmaterial is compounded, an effect of improving the charge/dischargecapacity and cycle characteristics may be expected even if the contentof sulfur becomes somewhat lower due to an influence of carbonconstituting the conductive carbon material. The content of sulfur insuch case may be lower than the above-mentioned sulfur content by about5.0% by mass. A total amount of carbon and sulfur in the organic sulfurmaterial is preferably 90% by mass or more, more preferably 92% by massor more, further preferably 94% by mass or more.

In addition, hydrogen (H) in the acrylic resin reacts with sulfur bycalcination to become hydrogen sulfide, which disappears from thesulfide. Therefore, a hydrogen content in the organic sulfur material ispreferably 1.8% by mass or less, further preferably 1.6% by mass orless. When it is 1.8% by mass or less, calcination (vulcanizationreaction) tends to be sufficient, and when it is 1.6% by mass or less,calcination (vulcanization reaction) tends to be more sufficient.Therefore, in this case, the charge/discharge capacity tends to improve.The hydrogen content is more preferably 1.0% by mass or less, furtherpreferably 0.6% by mass or less. In the present specification, a contentof an element is measured by elemental analysis according to aconventional method.

In the organic sulfur material, it is preferable that, in a Ramanspectrum detected by Raman spectroscopy, there exists a main peak around1450 cm⁻¹, and there exists other peaks around 485 cm⁻¹, around 1250cm⁻¹, and around 1540 cm⁻¹ in a range of 200 to 1800 cm⁻¹. In thisregard, the Raman spectra in Example 1 and Comparative examples 1 and 2are shown in FIG. 3. Besides, in the peak positions of the Ramanspectra, “around” means allowing an error range of ±50 cm⁻¹, especially±30 cm⁻¹.

Moreover, with respect to the organic sulfur material, in the Ramanspectrum, with a straight line connecting an intensity of 1000 cm⁻¹ andan intensity of 1800 cm⁻¹ being as a baseline, when a difference (I₁₄₅₀)between a peak intensity around 1450 cm⁻¹ and a corresponding baselineintensity and a difference (I₁₅₄₀) between a peak intensity around 1540cm⁻¹ and a corresponding baseline intensity are calculated, a value ofI₁₄₅₀/I₁₅₄₀ is preferably in a range of 1 to 4. In this regard, FIG. 4is shown as representing the values of I₁₄₅₀/I₁₅₄₀ in Examples 1 andComparative examples 1 and 2 so that they can be grasped on a graph. Thevalues of A/B shown in FIG. 4 are values of I₁₄₅₀/I₁₅₄₀.

The values of I₁₄₅₀/I₁₅₄₀ for Example 1 and Comparative examples 1 and 2are as shown in Table 1 below.

TABLE 1 Example Comparative example 1 1 2 I₁₄₅₀/I₁₅₄₀ 2.37 4.99 0.77

The value of I₁₄₅₀/I₁₅₄₀ is more preferably 1.20 or more, furtherpreferably 1.40 or more, further preferably 1.50 or more, furtherpreferably 2.00 or more, from the viewpoint of the effects of thepresent disclosure. On the other hand, the value is preferably 3.80 orless, more preferably 3.60 or less, further preferably 3.50 or less,further preferably 3.20 or less.

In the present disclosure, the Raman spectrum can be measured by RMP-320(excitation wavelength λ=532 nm, grating: 1800 gr/mm, resolution: 3cm⁻¹) manufactured by JASCO Corporation.

<Lithium-Ion Secondary Battery>

The organic sulfur material of the present disclosure can be used as anelectrode active material of a lithium-ion secondary battery, that is,as a positive electrode active material or a negative electrode activematerial. That is, an electrode for a lithium-ion secondary battery canbe produced in the similar manner as in the case of producing a generalelectrode for a lithium-ion secondary battery except that the organicsulfur material is used, and a lithium-ion secondary battery can befurther produced in the similar manner as in the case of producing ageneral lithium-ion secondary battery except that the electrode for alithium-ion secondary battery is used. The lithium-ion secondary batterythus produced has a large charge/discharge capacity and excellent cyclecharacteristics.

1. Using an Organic Sulfur Material as a Positive Electrode ActiveMaterial

The lithium-ion secondary battery of the present disclosure can beproduced according to a conventional method by using a negativeelectrode, an electrolyte, and, if desired, a member such as aseparator, in addition to a positive electrode comprising theabove-described organic sulfur material (positive electrode activematerial).

(Positive Electrode)

The positive electrode for a lithium-ion secondary battery can beproduced in the similar manner as for a general positive electrode for alithium-ion secondary battery except that the above-described organicsulfur material is used as a positive electrode active material. Forexample, the positive electrode can be produced by mixing a particulateorganic sulfur material with a conductive auxiliary agent, a binder, andsolvent to prepare a paste-like positive electrode material and applyingthe positive electrode material to a current collector, followed bydrying it. Moreover, as another method, the positive electrode can beproduced by, for example, kneading an organic sulfur material togetherwith a conductive auxiliary agent, a binder, and a small amount ofsolvent in a mortar or the like into a film shape, followed by pressingit to a current collector with a press machine or the like.

[Conductive Auxiliary Agent]

Examples of the conductive auxiliary agent include, for example, a vaporgrown carbon fiber (VGCF), a carbon powder, carbon black (CB), acetyleneblack (AB), ketjen black (KB), graphite, or a fine powder of a metalwhich is stable at a positive potential of aluminum, titanium and thelike. These conductive auxiliary agents can be used alone or two or morethereof can be used in combination.

[Binder]

Examples of the binder include polyvinylidene fluoride (PolyvinylideneDifluoride: PVDF), polytetrafluoroethylene (PTFE), a styrene-butadienerubber (SBR), polyimide (PI), polyamide-imide (PAI), carboxymethylcellulose (CMC), polyvinyl chloride (PVC), an acrylic resin, amethacrylic resin (PMA), polyacrylonitrile (PAN), a modifiedpolyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE),polypropylene (PP), and the like. These binders can be used alone or twoor more thereof can be used in combination.

[Solvent]

Examples of solvent include N-methyl-2-pyrrolidone,N,N-dimethylformaldehyde, alcohol, hexane, water, and the like. Thesesolvents can be used alone or two or more thereof can be used incombination.

[Compounding Amount]

A compounding amount of these materials constituting positive electrodesis not particularly limited, but it is preferable to compound, forexample, 2 to 100 parts by mass of a conductive auxiliary agent, 2 to 50parts by mass of a binder, and an appropriate amount of a solvent basedon 100 parts by mass of the organic sulfur material.

[Current Collector]

As a current collector, those commonly used for a positive electrode fora lithium-ion secondary battery may be used. For example, examples ofthe current collector include those composed of an aluminum foil, analuminum mesh, a punching aluminum sheet, an aluminum expand sheet, astainless steel foil, a stainless steel mesh, a punching stainless steelsheet, a stainless steel expand sheet, a foamed nickel, a nickelnon-woven fabric, a copper foil, a copper mesh, a punching copper sheet,a copper expand sheet, a titanium foil, a titanium mesh, a carbonnon-woven fabric, a carbon woven fabric, and the like. Among them, acurrent collector composed of a carbon non-woven fabric or a carbonwoven fabric composed of carbon with a high degree of graphitization isappropriate as a current collector when the organic sulfur material ofthe present disclosure is used as a positive electrode active material,since it does not comprise hydrogen and has a low reactivity withsulfur. As raw materials of a carbon fiber having a high degree ofgraphitization, various pitches (that is, by-products such as petroleum,coal, and coal tar) and a polyacrylonitrile fiber (PAN) which arematerials of the carbon fiber, and the like can be used. The currentcollector may be used alone or two or more thereof may be used incombination.

(Negative Electrode)

As a negative electrode material, a known metal lithium, carbon-basedmaterials such as graphite, silicon-based materials such as a siliconthin film, and alloy-based materials such as copper-tin and cobalt-tincan be used. When lithium-free materials, for example, carbon-basedmaterials, silicon-based materials, and alloy-based materials, among theabove-described negative electrode materials, are used as the negativeelectrode materials, there is an advantage that a short circuit betweenthe positive electrode and the negative electrode due to generation ofdendrite is less likely to occur. However, when these lithium-freenegative electrode materials are used in combination with the positiveelectrode of the present embodiment, neither the positive electrode northe negative electrode comprises lithium. Therefore, pre-dopingtreatment is required, in which lithium is previously inserted in eitheror both of the positive electrode and the negative electrode. Apre-doping method for lithium may comply with a known method. Forexample, examples of the method includes a method of inserting lithiumby an electrolytic doping method in which a semi-battery is assembledusing metallic lithium as a counter electrode to electrochemically dopelithium when lithium is doped into the negative electrode, and a methodof inserting lithium by an attaching pre-doping method in which ametallic lithium foil is left in an electrolytic solution after the foilis attached to the electrode to dope by diffusion of the lithium to theelectrode. In addition, the above-described electrolytic doping methodcan also be employed when lithium is pre-doped into the positiveelectrode. As the lithium-free negative electrode materials,silicon-based materials, which are high-capacity negative electrodematerials, are preferable, and among them, a thin-film silicon, whichhas a thin electrode thickness and has an advantage in terms of capacityper volume, is more preferable.

(Electrolyte)

As an electrolyte used in the lithium-ion secondary battery, those inwhich an alkali metal salt which is an electrolyte is dissolved in anorganic solvent can be used. As the organic solvent, it is preferable touse at least one selected from non-aqueous solvents such as ethylenecarbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate,ethyl methyl carbonate, dimethyl ether, γ-butyrolactone, andacetonitrile. As the electrolyte, LiPF₆, LiBF₄, LiAsF₆, LiCF₃SO₃, LiI,LiClO₄, and the like can be used. A concentration of the electrolyte maybe about 0.5 mol/L to 1.7 mol/L. Besides, the electrolyte is not limitedto one in a liquid state. For example, when the lithium-ion secondarybattery is a lithium polymer secondary battery, the electrolyte is in asolid state (for example, in a polymer gel state).

(Separator)

The lithium-ion secondary battery may comprise members such as aseparator in addition to the above-mentioned negative electrode,positive electrode, and electrolyte. The separator intervenes betweenthe positive electrode and the negative electrode to allow for movementof ions between the positive electrode and the negative electrode andprevents an internal short circuit between the positive electrode andthe negative electrode. If the lithium-ion secondary battery is of aclosed type, the separator is also required to have a function ofretaining an electrolytic solution. As the separator, it is preferableto use a thin-walled and microporous or non-woven film made ofpolyethylene, polypropylene, polyacrylonitrile, aramid, polyimide,cellulose, glass, and the like.

(Shape)

A shape of the lithium-ion secondary battery is not particularlylimited, and various shapes such as a cylindrical type, a laminatedtype, a coin type, and a button type can be used.

2. Using the Organic Sulfur Material as a Negative Electrode ActiveMaterial

The lithium-ion secondary battery of the present disclosure can beproduced according to a conventional method by using a positiveelectrode, an electrolyte, and, if desired, a member such as aseparator, in addition to a negative electrode comprising theabove-described organic sulfur material (negative electrode activematerial).

(Negative Electrode)

The negative electrode for a lithium-ion secondary battery can beproduced in the similar manner as for a general negative electrode for alithium-ion secondary battery except that the above-described organicsulfur material is used as a negative electrode active material. Forexample, the negative electrode can be produced by mixing a particulateorganic sulfur material with a conductive auxiliary agent, a binder, andsolvent to prepare a paste-like negative electrode material and applyingthe negative electrode material to a current collector, followed bydrying it. Moreover, as another method, the negative electrode can beproduced by, for example, kneading an organic sulfur material togetherwith a conductive auxiliary agent, a binder, and a small amount ofsolvent in a mortar or the like into a film shape, followed by pressingit to a current collector with a press machine or the like.

As the conductive auxiliary agent, binder and solvent, those similar asin the above-described case where the organic sulfur material is used asa positive electrode active material can be used in the similar manner,and the same applies to the current collector.

(Positive Electrode)

The positive electrode material is not particularly limited as long asit is, for example, a transition metal oxide comprising lithium or asolid solution oxide, or a substance that can electrochemically occludeand release lithium ions. Examples of the transition metal oxidecomprising lithium can include, for example, a Li/Co-based compositeoxide such as LiCoO₂, a Li/Ni/Co/Mn-based composite oxide such asLiNi_(x)Co_(y)Mn_(z)O₂, a Li/Ni-based composite oxide such as LiNiO₂, aLi/Mn-based composite oxide such as LiMn₂O₄, or the like. Examples ofthe solid solution oxide can include, for example,Li_(a)Mn_(x)Co_(y)Ni_(z)O₂ (1.150≤a≤1.430, 0.450≤x≤0.600, 0.100≤y≤0.150,0.200≤z≤0.280), LiMn_(x)Co_(y)Ni_(z)O₂ (0.300≤x≤0.850, 0.100≤y≤0.300,0.10≤z≤0.300), LiMn_(1.5)Ni_(0.5)O₄, and the like. These compounds maybe mixed alone or two or more thereof may be mixed in combination.

As for the electrolyte, the separator and the shape of a lithium-ionsecondary battery, those similar as in the above-described case wherethe organic sulfur material is used as a positive electrode activematerial can be used in the similar manner.

EXAMPLE

Although the present disclosure will be described based on Examples, itis not limited to Examples.

Various chemicals used in Examples and Comparative examples arecollectively shown below. They were purified according to a conventionalmethod as required.

<Materials Used for Test>

Acrylic resin 1: Spherical acrylic resin (ADVANCELL HB-2051 manufacturedby Sekisui Chemical Co., Ltd., particle size: 20 μm)

Acrylic resin 2: Spherical acrylic resin consisting of polymethylmethacrylate (TECHPOLYMER MB-8 (spherical acrylic resin consisting of ahomopolymer of methyl methacrylate) manufactured by Sekisui Kasei Co.,Ltd., particle size: 8 μm)

Acrylic resin 3: Spherical acrylic resin consisting of crosslinkedpolymethyl methacrylate (TECHPOLYMER MB30X-5 (spherical acrylic resinconsisting of a copolymer of methyl methacrylate and ethylene glycoldimethacrylate) manufactured by Sekisui Kasei Co., Ltd., particle size:5 μm)

Acrylic resin 4: Spherical acrylic resin consisting of crosslinkedpolybutyl methacrylate (TECHPOLYMER BM30X-8 (spherical acrylic resinconsisting of a copolymer of butyl methacrylate and ethylene glycoldimethacrylate) manufactured by Sekisui Kasei Co., Ltd., particle size:8 μm)

Acrylic resin 5: Spherical acrylic resin consisting of crosslinkedpolymethyl methacrylate (TECHPOLYMER MB30X-8 (spherical acrylic resinconsisting of a copolymer of methyl methacrylate and ethylene glycoldimethacrylate) manufactured by Sekisui Kasei Co., Ltd., particle size:8 μm)

Acrylic resin 6: Spherical acrylic resin consisting of crosslinkedpolymethyl methacrylate (TECHPOLYMER MB30X-20 (spherical acrylic resinconsisting of a copolymer of methyl methacrylate and ethylene glycoldimethacrylate) manufactured by Sekisui Kasei Co., Ltd., particle size:20 μm)

Acrylic resin 7: Porous acrylic resin consisting of crosslinkedpolymethyl methacrylate (TECHPOLYMER MBP-8 (porous acrylic resinconsisting of a copolymer of methyl methacrylate and ethylene glycoldimethacrylate) manufactured by Sekisui Kasei Co., Ltd.), particlesDiameter: 8 μm)

Acrylic resin 8: Spherical acrylic resin consisting of polymethylmethacrylate (PARAPET GF-P (spherical acrylic resin consisting of ahomopolymer of methyl methacrylate) manufactured by Kuraray Co., Ltd.,particle size: 270 μm)

Acrylic resin 9: Spherical acrylic resin consisting of crosslinkedpolybutyl methacrylate (TECHPOLYMER BM30X-5 (spherical acrylic resinconsisting of a copolymer of butyl methacrylate and ethylene glycoldimethacrylate) manufactured by Sekisui Kasei Co., Ltd., particle size:5 μm)

Acrylic resin 10: Spherical acrylic resin consisting of crosslinkedpolybutyl methacrylate (TECHPOLYMER BM30X-12 (spherical acrylic resinconsisting of a copolymer of butyl methacrylate and ethylene glycoldimethacrylate) manufactured by Sekisui Kasei Co., Ltd., particle size:12 μm)

Acrylic resin 11: Spherical acrylic resin consisting of crosslinkedpolybutyl methacrylate (GANZPEARL GB-15S (spherical acrylic resinconsisting of a copolymer of butyl methacrylate and ethylene glycoldimethacrylate) manufactured by Aica Kogyo Co., Ltd., particle size: 15μm)

High cis BR: High cis butadiene rubber (BR150L manufactured by UbeIndustries, Ltd., cis 1,4 bond content=98% by mass)

PAN: Polyacrylonitrile (manufactured by Sigma-Aldrich, particle size: 8μm)

Sulfur: Precipitated sulfur manufactured by Tsurumi Chemical IndustryCo., Ltd.

Example 1 <Production of Raw Materials>

According to the formulation shown in Table 3, materials were mixed in ablender to obtain a raw material for calcination (calcinated rawmaterial).

(Reaction Apparatus)

A reaction apparatus 1 shown in FIG. 1 was used for calcinating a rawmaterial. The reaction apparatus 1 comprises a reaction vessel 3 with anouter diameter of 60 mm, an inner diameter of 50 mm, and a height of 300mm made of a quartz glass having a bottomed cylindrical shape foraccommodating and calcinating a raw material 2, a lid 4 made of siliconefor closing an upper opening of the reaction vessel 3, one aluminaprotective tube 5 penetrating the lid 4 (“Alumina SSA-S” manufactured byNikkato Corporation, outer diameter: 4 mm, inner diameter: 2 mm, length:250 mm), a pair of gas introduction tube 6 and gas discharge tube 7 (forboth, “Alumina SSA-S” manufactured by Nikkato Corporation, outerdiameter: 6 mm, inner diameter: 4 mm, length: 150 mm), and an electricfurnace 8 for heating the reaction vessel 3 from the bottom side (acrucible furnace, opening width: φ80 mm, heating height: 100 mm).

The alumina protective tube 5 is formed to have a length below the lid 4that reaches the raw material 2 accommodated in the bottom of thereaction vessel 3, and a thermocouple 9 is inserted therein. The aluminaprotective tube 5 is used as a protective tube for the thermocouple 9.The tip of the thermocouple 9 is inserted into the raw material 2 whilebeing protected by the closed tip of the alumina protective tube 5 andfunctions to measure temperature of the raw material 2. An output of thethermocouple 9 is input to a temperature controller 10 of the electricfurnace 8 as shown by the arrow with solid line in the figure, and thetemperature controller 10 functions to control the heating temperatureof the electric furnace 8 based on this input from the thermocouple 9.

The lower ends of the gas introduction tube 6 and the gas discharge tube7 are formed so as to protrude downward from the lid 4 by 3 mm. Ar(Argon) gas is continuously supplied from a gas supply system (notshown) to the gas introduction tube 6. In addition, the gas dischargetube 7 is connected to a trap tank 12 accommodating a sodium hydroxideaqueous solution 11. An exhaust gas going out of the reaction vessel 3through the gas discharge tube 7 is once passed through the sodiumhydroxide aqueous solution 11 in the trap tank 12 and then discharged tothe outside. Therefore, even if the exhaust gas contains a hydrogensulfide gas generated by a vulcanization reaction, the hydrogen sulfidegas is neutralized with the sodium hydroxide aqueous solution andremoved from the exhaust gas.

(Calcinating Step)

First, Ar gas was continuously supplied at a flow rate of 80 mL/min fromthe gas supply system with the raw material 2 being accommodated in thebottom of the reaction vessel 3, and 30 minutes after the initiation ofthe supply, heating by the electric furnace 8 was initiated. The heatingwas performed at a temperature rising rate of 150° C./h. And when thetemperature of the raw material reached the calcinating temperature inTable 3 (400° C.), calcination was performed for 2 hours whilemaintaining the calcinating temperature of 400° C. Next, while adjustingthe flow rate of Ar gas, temperature of a reaction product was naturallycooled to 25° C. under an Ar gas atmosphere, and then the reactionproduct was taken out from the reaction vessel 3.

(Removal of Unreacted Sulfur)

The following steps were performed in order to remove unreacted sulfur(elemental sulfur in a free state) remaining in the product after thecalcinating step. That is, the product was pulverized in a mortar, and 2g of the pulverized product was accommodated in a glass tube oven andheated at 250° C. for 3 hours while being sucked by a vacuum to obtainan organic sulfur material in which unreacted sulfur were removed (orwhich comprises a small amount of unreacted sulfur only). Thetemperature rising rate was set to be 10° C./min.

(Classification)

In order to remove coarse particles of a calcinated product,classification was performed by using a 32 μm mesh stainless steel sieveto obtain an organic sulfur material 1.

<Production of Lithium-Ion Secondary Battery>

A lithium-ion secondary battery was produced as follows.

(Positive Electrode)

The organic sulfur material 1 as an active material, acetylene black asa conductive auxiliary agent, and acrylic resin as a binder were used.They were weighed so as to have a ratio of the active material:theconductive auxiliary agent:the binder=90:5:5 (mass ratio), placed in acontainer, stirred and mixed with a rotating and revolving mixer(ARE-250 manufactured by Thinky Corporation) using milliQ water as adispersant to produce a uniform slurry. The produced slurry was coatedonto an aluminum foil having a thickness of 20 μm using an applicatorhaving a slit width of 60 μm, and a positive electrode compressed with aroll press was dried by heating at 120° C. for 3 hours with a dryer,followed by punched to φ11 to obtain an electrode (a positiveelectrode). Then, a weight of the positive electrode was measured, andan amount of the active material in the electrode was calculated fromthe ratio mentioned above.

(Negative Electrode)

As a negative electrode, a metallic lithium foil (a disk shape foil witha diameter of 14 mm and a thickness of 500 μm, manufactured by HonjoMetal Co., Ltd.) was used.

(Electrolytic Solution)

As an electrolytic solution, a non-aqueous electrolyte in which LiPF₆was dissolved in a mixed solvent of ethylene carbonate and diethylcarbonate was used. Ethylene carbonate and diethyl carbonate were mixedat a volume ratio of 1:1. A concentration of LiPF₆ in the electrolyticsolution was 1.0 mol/L.

(Lithium-Ion Secondary Battery)

A coin battery was produced using the positive electrode and thenegative electrode described above. Specifically, in a dry room, aseparator (Celgard 2400 manufactured by Celgard, LLC, polypropylenemicroporous film having a thickness of 25 μm) and a glass non-wovenfabric filter (thickness: 440 μm, GA100 manufactured by ADVANTEC) wereinterposed between the positive electrode and the negative electrode toform an electrode body battery. This electrode body battery wasaccommodated in a battery case composed of a stainless-steel container(CR2032 type coin battery member, manufactured by Hohsen Corp.). Theabove-described electrolytic solution was injected into the batterycase. The battery case was sealed with a caulking machine to produce alithium-ion secondary battery of Example 1.

Examples 2 to 16 and Comparative Examples 1 to 2

Each calcinated raw material, organic sulfur material, and lithium-ionsecondary battery were produced in the same manner as in Example 1except that appropriate changes were made according to the compoundingformulations and conditions in Tables 3 and 4.

<Discharge Capacity and Measurement of Capacity Retention>

The coin-type lithium-ion secondary battery produced in each Example andComparative example was charged and discharged with a current valuecorresponding to 50 mA per 1 g of a positive electrode active materialunder a condition of a test temperature at 30° C. for the first to9^(th) time. It was charged and discharged with a current valuecorresponding to 250 mA for the 10^(th) to 30^(th) time. A dischargefinal voltage was set to be 1.0 V, and a charge final voltage was set tobe 3.0 V. In addition, the charging/discharging was repeated, and the10^(th) and 30^(th) battery discharge capacities (mAh) were observed.

The second discharge capacity (mAh/g) was regarded as an initialcapacity. It can be evaluated that the larger the initial capacity is,the larger the charge/discharge capacity of the lithium-ion secondarybattery is, which is preferable. Moreover, from the 10^(th) dischargecapacity DC₁₀ (mAh/g) and the 30^(th) discharge capacity DC₃₀ (mAh/g), acapacity retention (%) was calculated by the following equation (a):

Capacity retention (%)=(DC₃₀/DC₁₀)×100  (a)

As described above, it can be said that the higher the capacityretention is, the more excellent the cycle characteristics of thelithium-ion secondary battery is.

<Elemental Analysis> (Method)

Each mass of carbon, hydrogen, sulfur, and nitrogen was measured using afully automatic elemental analyzer, vario MICRO cube manufactured byElementar, and each mass ratio (%) was calculated.

(Acrylic Resin)

Elemental analysis was performed on the acrylic resin used in Examples.The results are as shown in the table below. The mass ratios of C(carbon), H (hydrogen), N (nitrogen), and S (sulfur) are actual values.It is estimated that the remainder obtained by subtracting these actualvalues from the total amount (100%) is substantially a mass ratio of O(oxygen).

TABLE 2 Acrylic resin 1 2 3 4 5 6 7 8 9 10 11 C 61.90% 60.40% 60.70%66.40% 60.80% 60.50% 60.70% 60.20% 66.50% 66.40% 65.90% H  8.09%  8.10% 7.78%  9.18%  7.75%  7.72%  7.70%  8.05%  9.17%  9.16%  8.98% N    0%   0%    0%    0%    0%    0%    0%    0%    0%    0%    0% O 29.53%31.50% 31.50% 24.30% 31.50% 31.80% 31.60% 31.80% 24.30% 24.30% 25.12% S   0%    0%    0%    0%    0%    0%    0%    0%    0%    0%    0%

(Organic Sulfur Material)

Elemental analysis was performed on the organic sulfur materialsproduced in Examples and Comparative examples. The results are shown inTables 3 and 4.

<IR Spectrum>

An IR spectrum was measured by the above-described method. The resultsfor acrylic resin 1 (Example 1), acrylic resin 2 (Example 2), acrylicresin 3 (Example 3), and acrylic resin 4 (Example 4) are shown in FIG.2.

<Raman Spectrum>

A Raman spectrum was measured by the above-described method. The resultsfor organic sulfur materials in Example 1 and Comparative examples 1 and2 are shown in FIG. 3.

TABLE 3 Example Comparative example 1 2 3 4 5 6 7 8 1 2 ElectrodeCalcinated raw material Compounding (part by mass) Acrylic resin 1 100 —— — — — — — — — Acrylic resin 2 — 100 — — — — — — — — Acrylic resin 3 —— 100 — — — — — — — Acrylic resin 4 — — — 100 — — — — — — Acrylic resin5 — — — — 100 — — — — — Acrylic resin 6 — — — — — 100 — — — — Acrylicresin 7 — — — — — — 100 — — — Acrylic resin 8 — — — — — — — 100 — — Highcis BR — — — — — — — — 100 — PAN 100 Sulfur 300 300 300 300 300 300 300300 300 300 Calcination Calcinating temperature (° C.) 400 400 400 400400 400 400 400 400 400 Elemental analysis (%) C 41.5 41.1 40.5 40.139.0 41.0 39.9 41.4 44.0 39.2 H 0.56 0.72 0.31 0.21 0.45 0.26 0.68 0.350.39 0.91 N 0.02 0.04 0.03 0.02 0.03 0.05 0.04 0.03 0.26 13.9 S 56.756.6 58.4 62.0 60.1 59.8 59.3 55.1 57.6 43.3 Evaluation on batteryDischarge capacity (mAh/g) First 823 857 858 879 880 853 927 797 855 705Second 611 646 642 656 651 619 679 608 543 613 10^(th) 501 539 527 521530 476 511 520 401 512 30^(th) 501 526 518 503 515 455 476 518 333 499Capacity retention (%) 100 98 98 97 97 96 93 99 83 97

TABLE 4 Example 9 10 11 12 13 14 15 16 Electrode Calcinated raw materialCompounding (part by mass) Acrylic resin 9 100 — — 100 100 100 100 100Acrylic resin 10 — 100 — — — — — — Acrylic resin 11 — — 100 — — — — —High cis BR — — — — — — — — PAN — — — — — — — — Sulfur 300 300 300 200500 1000 300 300 Calcination Calcinating temperature (° C.) 400 400 400400 400 400 370 430 Elemental analysis (%) C 38.4 39.6 40.5 41.2 40.340.8 40.5 40.2 H 0.25 0.39 0.49 0.43 0.29 0.38 0.37 0.19 N 0.03 0 0 0.050 0.05 0 0.12 S 63.8 61.6 57.5 57.3 59.5 59.9 59.4 61.2 Evaluation onbattery Discharge capacity (mAh/g) First 922 901 850 864 842 819 880 825Second 701 691 636 647 620 605 661 613 10^(th) 581 579 513 528 532 497545 508 30^(th) 577 575 508 518 532 497 545 508 Capacity retention (%)99 98 99 98 100 100 100 100

From Tables 3 and 4, it can be seen that a higher initial capacity(mAh/g) is shown and the capacity retention (%) is maintained at ahigher level in Examples, compared with Comparative example 1.Comparative example 2 shows high initial capacity and capacityretention, but it uses expensive polyacrylonitrile as a raw material,and thus it is less likely to be provided at a low cost. According tothe organic sulfur material of the present disclosure, a lithium-ionsecondary battery having a high initial capacity and a good capacityretention can be provided inexpensively.

EXPLANATION OF NUMERALS

-   1. Reaction apparatus-   2. Raw material-   3. Reaction vessel-   4. Silicone lid-   5. Alumina protective tube-   6. Gas introduction tube-   7. Gas discharge tube-   8. Electric furnace-   9. Thermocouple-   10. Temperature controller-   11. Sodium hydroxide aqueous solution-   12. Trap tank-   A. Difference between peak intensity around 1450 cm⁻¹ and    corresponding baseline intensity-   B. Difference between peak intensity around 1540 cm⁻¹ and    corresponding baseline intensity

1. An organic sulfur material comprising: a sulfur-modified acrylicresin, wherein an acrylic resin has peaks around 756 cm⁻¹, around 1066cm⁻¹, around 1150 cm⁻¹, around 1245 cm⁻¹, around 1270 cm⁻¹, around 1453cm⁻¹, and around 1732 cm⁻¹ in an FT-IR spectrum.
 2. The organic sulfurmaterial of claim 1, wherein the peak around 1150 cm⁻¹ and the peakaround 1732 cm⁻¹ are larger than the remaining peaks.
 3. The organicsulfur material of claim 1, wherein the FT-IR spectrum further has peaksaround 846 cm⁻¹, around 992 cm⁻¹, around 1196 cm⁻¹, around 2955 cm⁻¹,and around 2996 cm⁻¹.
 4. The organic sulfur material of claim 1, whereinmass ratios of carbon, hydrogen, nitrogen, and sulfur in a total amountof the acrylic resin are 60.0 to 70.0%, 7.5 to 9.5%, 0.0%, and 0.0 to1.0%, respectively.
 5. The organic sulfur material of claim 1, whereinthe modification is performed by calcination under a non-oxidizingatmosphere.
 6. The organic sulfur material of claim 1, wherein aparticle size of the acrylic resin is 0.1 to 300.0 μm.
 7. The organicsulfur material of claim 1, wherein the acrylic resin has a porousstructure.
 8. The organic sulfur material of claim 1, wherein, in aRaman spectrum detected by Raman spectroscopy, there exists a main peakaround 1450 cm⁻¹, and there exists other peaks around 485 cm⁻¹, around1250 cm⁻¹, and around 1540 cm⁻¹ in a range of 200 to 1800 cm⁻¹.
 9. Theorganic sulfur material of claim 8, wherein, in the Raman spectrum, witha straight line connecting an intensity of 1000 cm⁻¹ and an intensity of1800 cm⁻¹ being as a baseline, when a difference (I₁₄₅₀) between a peakintensity around 1450 cm⁻¹ and a corresponding baseline intensity and adifference (I₁₅₄₀) between a peak intensity around 1540 cm⁻¹ and acorresponding baseline intensity are calculated, a value of I₁₄₅₀/I₁₅₄₀is in a range of 1 to
 4. 10. The organic sulfur material of claim 1,wherein an amount of sulfur in the organic sulfur material is 50.0% bymass or more.
 11. An electrode comprising the organic sulfur material ofclaim
 1. 12. A lithium-ion secondary battery comprising the electrode ofclaim
 11. 13. A method of producing an organic sulfur material, themethod comprising steps of: (1) preparing an acrylic resin, and (2)modifying the acrylic resin with sulfur, wherein the acrylic resin haspeaks around 756 cm⁻¹, around 1066 cm⁻¹, around 1150 cm⁻¹, around 1245cm⁻¹, around 1270 cm⁻¹, around 1453 cm⁻¹, and around 1732 cm⁻¹ in anFT-IR spectrum.
 14. The method of claim 13, wherein the modification isperformed by calcination under a non-oxidizing atmosphere.
 15. Themethod of claim 13, wherein an amount of sulfur with respect to theacrylic resin is 50 to 1000 parts by mass based on 100 parts by mass ofthe acrylic resin.
 16. The method of claim 14, wherein a temperature ofthe calcination is 250 to 550° C.
 17. The method of claim 13, wherein aparticle size of the acrylic resin is 0.1 to 300.0 μm.
 18. The method ofclaim 13, wherein the acrylic resin has a porous structure.
 19. A methodof producing an electrode, the method further comprising, afterproducing the organic sulfur material by the method of claim 13, a stepof: (3) preparing an electrode using the organic sulfur material by aconventional method.
 20. A method of producing a lithium-ion secondarybattery, the method further comprising, after producing the electrode bythe method of claim 19, a step of: (4) preparing a lithium-ion secondarybattery using the electrode by a conventional method.